Mill base composition and uv curable ink composition comprising same

ABSTRACT

A mill base composition includes a compound comprising a divinyl ester of a dicarboxylic acid, a dispersing agent, and a pigment. The divinyl ester of the carboxylic acid includes from 2 to about 8 carbon atoms. The mill base composition is subjected to milling with milling beads to produce a milled mill base composition that functions as a pigment concentrate that may be added to an ink vehicle to form an ink composition suitable for use in inkjet ink devices. The milled mill base composition is particularly suited for UV curable ink compositions. A UV curable ink composition includes the pigment concentrate, one or more UV curable monomers, and one or more UV initiators.

CROSS-REFERENCE TO RELATED APPLICATIONS

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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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BACKGROUND

Inkjet printers are now very common and affordable and allow one toobtain decent print quality. They are used in home printing, officeprinting and commercial printing. The growth of inkjet printing is aresult of a number of factors including reductions in cost of inkjetprinters and improvements in print resolution and overall print quality.A continued demand in inkjet printing has resulted in a need to produceimages of high quality, high permanence and high durability whilemaintaining a reasonable cost.

Inkjet printing is a popular method of non-contact printing on a broadselection of substrates. One popular variety of inkjet printing involvesusing UV curable inkjet inks, which enable high printing speed. UVcurable inkjet inks have relatively good adhesion on variety ofsubstrates and they have low Volatile Organic Compound (VOC) content.There are two types of UV inks, radical curing inks and cationic curinginks or hybrids thereof. The majority of inks currently used in theindustry are radical inks although some cationic inks exist.

One of the major shortcomings of UV curable components is that amajority of such components have intrinsic high viscosity, which limitsthe ink design space and the ability to formulate inks suitable forinkjet application. This problem is common for both radical UV curablecomponents and cationic UV curable components. Mill bases are employedin the milling of pigment particles to further the dispersion of theparticles in a resulting ink. The mill bases used in the preparation ofUV curable inkjet inks are characterized by relatively high pigmentload, which is at least 20% by weight pigment content in the mill base.

DETAILED DESCRIPTION

There is a need in the industry to have a milling vehicle component thatcan be used in the preparation of both types of UV curable inks and inthe preparation of hybrid UV inks The pigments are usually milled in aUV curable carrier with beads having a diameter of about 0.65millimeters (mm), for example. By reducing the size of pigment particlesduring a milling process, ink jetting reliability and colloidalstability of the ink dispersion may be improved. Milling a mill basewith beads much lower than the above would further this goal. Themilling vehicle component should enable milling in a high pigment loadenvironment where at least one step in the milling process is carriedout with a milling media having a diameter not larger than about 0.3millimeters (mm) without a substantial negative effect on the quality ofinks obtained from a mill base composition.

Examples of mill base compositions in accordance with the principlesdescribed herein comprise a divinyl ester of a dicarboxylic acid as amilling vehicle component. Examples of mill base compositions inaccordance with the principles described herein allow for millingpigments with relatively smaller milling media. Mill base compositionsin accordance with the principles described herein may be subjected toan initial milling step using milling beads larger than 0.45 mm,followed by a milling step with milling beads having a diameter nolarger than about 0.3 mm. As a consequence of effectively reducing thesize of pigment particles, ink jetting reliability and colloidalstability of the ink dispersion are improved. In addition to allowingfor high pigment loading with relatively smaller milling media, examplesof mill base compositions in accordance with the principles describedherein allow small pigment particle size, narrow particle sizedistribution, good rheology, high curing speed and excellent colorstrength when formulated in inkjet inks By reducing the size of pigmentparticles during a milling process, ink jetting reliability andcolloidal stability of the ink dispersion may be improved.

Examples of mill base compositions in accordance with the principlesdescribed herein may be used in the preparation of UV curable inkjetinks including radical, cationic and cationic-radical hybrid UV curableinkjet inks The inkjet inks produced using milled mill base compositionsin accordance with the principles described herein exhibit improvedinkjet ink and mill base rheology, reduced mill base and inkjet inkviscosity, and improved inkjet ink stability (aging). Moreover, theinkjet inks produced using milled mill base compositions describedherein enable stable cationic radical hybrid inkjet ink formulations.Furthermore, examples of mill base compositions described herein have aminimal, if any, negative effect on ink qualities. Using milled millbase compositions in accordance with the principles described herein toprepare inkjet ink compositions does not reduce other qualities of anink composition compared to similar inks made from a milled mill basecomposition that does not comprise a compound comprising a divinyl esterof a dicarboxylic acid.

Some examples in accordance with the principles described herein aredirected to mill base compositions that comprise a compound comprising adivinyl ester of a dicarboxylic acid wherein the dicarboxylic acidcomprises from 2 to about 8 carbon atoms, a dispersing agent, and apigment.

The phrase “mill base composition” means a composition comprisingpigment particles, dispersing agent, and a milling vehicle. The pigmentparticles are to be reduced to a size suitable for combining with an inkvehicle to produce an ink composition.

The phrase “a compound comprising a divinyl ester of a dicarboxylicacid” refers to a compound that contains at least two vinyl esterifiedcarboxylic acid groups. In some examples, a compound comprising adivinyl ester of a dicarboxylic acid comprises two vinyl esterifiedcarboxylic acid groups.

The phrase “dicarboxylic acid” refers to an organic acid that comprises2 to 8 carbon atoms, or 2 to 7 carbon atoms, or 2 to 6 carbon atoms, or2 to 5 carbon atoms, or 2 to 4 carbon atoms, or 2 to 3 carbon atoms, or3 to 8 carbon atoms, or 3 to 7 carbon atoms, or 3 to 6 carbon atoms, or3 to 5 carbon atoms, or 3 to 4 carbon atoms, or 4 to 8 carbon atoms, or4 to 7 carbon atoms, or 4 to 6 carbon atoms, or 4 to 5 carbon atoms, or5 to 8 carbon atoms, or 5 to 7 carbon atoms, or 5 to 6 carbon atoms, or6 to 8 carbon atoms, or 6 to 7 carbon atoms, or 7 to 8 carbon atoms, forexample, and two carboxylic acid groups, that is, —COOH groups, forexample, where the number of carbon atoms of the carboxylic acid groupis included in the number of carbon atoms referred to above.Dicarboxylic acids that may be employed in examples in accordance withthe principles described herein include, but are not limited to, oxalicacid, malonic acid, succinic acid, glutaric acid, adipic acid,cyclohexyl dicarboxylic acid, phthalic acid, terephthalic acid, andpimelic acid, for example.

The phrase “divinyl ester” refers to vinyl moieties that are attached totwo carboxylic acid groups of the dicarboxylic acid where the form ofattachment is an ester bond. The phrase “vinyl moieties” refers toorganic moieties that comprise at least one carbon-carbon double bond.The vinyl moiety may comprise one or more substituents in place of oneor more of the hydrogens of the vinyl moiety. Such substituents include,by way of illustration and not limitation, alkyl groups, an aryl groups,and an alkaryl groups, for example.

The term “alkyl” as used herein means a branched, unbranched, or cyclicsaturated hydrocarbon group, which typically, although not necessarily,contains from 1 to about 20 carbon atoms, or 1 to about 15 carbon atoms,or 1 to about 10 carbon atoms, or 1 to about 5 carbon atoms, forexample. Alkyl groups include, but are not limited to, methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, octyl, and decyl, forexample, as well as cycloalkyl groups such as cyclopentyl, andcyclohexyl, for example. In some examples, the alkyl group may comprisea halo group (chloro, bromo, iodo, fluoro) substitution in place of,e.g., one or more of the hydrogens of the alkyl group.

The term “aryl” means a group containing a single aromatic ring ormultiple aromatic rings that are fused together, directly linked, orindirectly linked (such that the different aromatic rings are bound to acommon group such as a methylene or ethylene moiety). Aryl groupsdescribed herein may contain, but are not limited to, about 5 to about20 carbon atoms, or about 5 to about 15 carbon atoms, or about 5 to 10carbon atoms or more. Aryl groups include, for example, phenyl,naphthyl, anthryl, phenanthryl, and biphenyl.

The term “aromatic” as used herein includes monocyclic rings, bicyclicring systems, and polycyclic ring systems, in which the monocyclic ring,or at least a portion of the bicyclic ring system or polycyclic ringsystem, is aromatic (exhibits, e.g., π-conjugation). The monocyclicrings, bicyclic ring systems, and polycyclic ring systems of thearomatic ring systems may include carbocyclic rings (each ring atom is acarbon atom) and/or heterocyclic rings (at least one ring atom is notcarbon and is a heteroatom).

The term “alkaryl” includes those moieties that comprise both an alkylgroup and an aryl group.

Examples of vinyl moieties include, but are not limited to, thosemoieties represented by the formula:

wherein R′, R″, and R′″ are, but are not limited to, hydrogen, alkyl,aryl, and alkaryl, for example. In some examples in accordance with theprinciples described herein, R′, R″, and R′″ are hydrogen, or one of R′,R″, and R′″ is methyl and the others are hydrogen, or R′ is methyl andR″ and R′″ are hydrogen, for example.

In some examples in accordance with the principles described herein, thecompound comprising a divinyl ester of the dicarboxylic acid has aviscosity of about 0.5 to about 15 millipascal seconds (mpas), or about0.5 to about 10 mpas, or about 0.5 to about 5 mpas, or about 1 to about15 mpas, or about 1 to about 10 mpas, or about 1 to about 5 mpas, forexample. In some examples in accordance with the principles describedherein, the divinyl ester of the dicarboxylic acid has a vapor pressureless than about 0.1 millibar (mbar), or less than about 0.05 mbar, orless than about 0.01 mbar. In some examples in accordance with theprinciples described herein, the divinyl ester of the dicarboxylic acidhas a boiling point greater than about 150° C., or greater than about170° C., or greater than about 230° C.

An amount of the compound comprising a divinyl ester of a dicarboxylicacid in the mill base composition is chosen to be at an optimum amountthat enables high pigment loading, good ink rheology, low viscosity andimproved storage stability. In some examples in accordance with theprinciples described herein, the amount (by weight) of divinyl ester inthe mill base composition is about 30% to about 60%, or about 30% toabout 55%, or about 30% to about 50%, or about 30% to about 45%, orabout 30% to about 40%, or about 30% to about 35%, or about 35% to about60%, or about 35% to about 55%, or about 35% to about 50%, or about 35%to about 45%, or about 35% to about 40%, or about 40% to about 60%, orabout 40% to about 55%, or about 40% to about 50%, or about 40% to about45%, or about 45% to about 60%, or about 45% to about 55%, or about 45%to about 50%, or about 50% to about 60%, for example.

In some examples in accordance with the principles described herein thecompound comprising a divinyl ester of the dicarboxylic acid is selectedfrom the group consisting of adipic acid divinyl ester (AVES),cyclohexyl dicarboxylic acid divinyl ester (CHDVES), and terephthalicacid divinyl ester (TVES), and combinations thereof. In some examples inaccordance with the principles described herein, the dicarboxylic aciddivinyl ester is AVES, which has a viscosity of 2.5 mpas at 30° C., avapor pressure less than 0.01 mbar and a boiling point greater than 230°C.

The mill base composition in accordance with the principles describedherein includes a dispersing agent. The choice of a dispersing agent isdependent on one or more factors such as, for example, facilitation ofdeaggregation of pigment agglomerates and stabilization of pigmentparticles during a milling process, the size of the milled pigmentparticles, and the physical properties of the milled composition.

In some examples in accordance with the principles described herein, thedispersing agent is, by way of illustration and not limitation, apolyester, a polyurethane, or a polyalkylene imine, for example, whichmay comprise one or more ionic groups, acidic groups, and alcoholgroups, for example. By way of illustration and not limitation, specificexamples of polyesters that may be employed as dispersing agents inaccordance with the principles described herein include SOLSPERSE® 32000and SOLSPERSE® J200 (both from Lubrizol Corporation, Rancho SantaMargarita Calif.), for example. By way of illustration and notlimitation, examples of polyurethanes that may be employed as dispersingagents in accordance with the principles described herein includeSOLSPERSE® 76500 (Lubrizol Corporation), for example. By way ofillustration and not limitation, specific examples of polyalkyleneimines that may be employed as dispersing agents in accordance with theprinciples described herein include SOLSPERSE® 39000 (LubrizolCorporation), for example.

In some examples in accordance with the principles described herein, theamount (by weight) of dispersing agent in the mill base composition isabout 5% to about 50%, or about 5% to about 40%, or about 5% to about30%, or about 5% to about 20%, or about 5% to about 10%, or about 10% toabout 50%, or about 10% to about 40%, or about 10% to about 30%, orabout 10% to about 20%, or about 20% to about 50%, or about 20% to about40%, or about 20% to about 30%, or about 30% to about 50%, or about 30%to about 40%, or about 40% to about 50%, for example, of the mill basecomposition.

In some examples in accordance with the principles described herein, thedispersing agent further comprises an organic solvent, which may besoluble in water or miscible in water. The dispersing agent may includeorganic solvents as diluents to adjust viscosity of the dispersing agentto a level that is suitable for milling the mill base composition suchas, for example, where the viscosity of the active reagent of thedispersant agent is too high or the dispersing agent is too difficult tohandle. A single organic solvent or a combination of two or more organicsolvents may be used.

In some examples, the organic solvent is a polar organic solvent havingabout 2 to about 50 carbon atoms, or about 2 to about 40 carbon atoms,or about 2 to about 30 carbon atoms, or about 2 to about 20 carbonatoms, or about 2 to about 10 carbon atoms, or about 5 to about 50carbon atoms, or about 5 to about 40 carbon atoms, or about 5 to about30 carbon atoms, or about 5 to about 20 carbon atoms, or about 5 toabout 10 carbon atoms, or about 10 to about 50 carbon atoms, or about 10to about 40 carbon atoms, or about 10 to about 30 carbon atoms, or about10 to about 20 carbon atoms, or about 10 to about 15 carbon atoms. Insome examples, the organic solvent further has 1 to about 20heteroatoms, or about 1 to about 15 heteroatoms, or about 1 to about 10heteroatoms, or about 1 to about 5 heteroatoms, or about 2 to about 20heteroatoms, or about 2 to about 15 heteroatoms, or about 2 to about 10heteroatoms, or about 2 to about 5 heteroatoms, or about 3 to about 20heteroatoms, or about 3 to about 15 heteroatoms, or about 3 to about 10heteroatoms, or about 3 to about 5 heteroatoms, or about 4 to about 20heteroatoms, or about 4 to about 15 heteroatoms, or about 4 to about 10heteroatoms, or about 4 to about 5 heteroatoms, or about 5 to about 20heteroatoms, or about 5 to about 15 heteroatoms, or about 5 to about 10heteroatoms, for example. The heteroatoms may be in the form of one ormore alcohol moieties, ether moieties, ketone moieties, aldehydemoieties, amine moieties, and amide moieties, for example.

In some examples the organic solvent has a boiling point of about 120°C. to about 250° C., or about 120° C. to about 225° C., or about 120° C.to about 200° C., or about 120° C. to about 175° C., or about 120° C. toabout 150° C., or about 130° C. to about 250° C., or about 130° C. toabout 225° C., or about 130° C. to about 200° C., or about 130° C. toabout 180° C., or about 130° C. to about 160° C., or about 140° C. toabout 230° C., or about 140° C. to about 200° C., or about 140° C. toabout 180° C., or about 140° C. to about 160° C., or about 150° C. toabout 250° C., or about 150° C. to about 225° C., or about 150° C. toabout 200° C., or about 150° C. to about 175° C., for example.

In some examples, the organic solvent is, by way of illustration and notlimitation, an ester of a carboxylic acid (for example, acetic acid,propanoic acid, butanoic acid, or pentanoic acid) and an alcohol (forexample, methanol, ethanol, propanol, isopropanol, butanol, isobutanol,sec-butanol, t-butanol, pentanol, hexanol, cyclohexanol or benzylalcohol); a polyhydric alcohol (for example, ethylene glycol, diethyleneglycol, triethylene glycol, polyethylene glycol, propylene glycol,dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol,pentanediol, glycerol, hexanetriol, or thiodiglycol); a glycolderivative (for example, ethylene glycol monomethyl ether, ethyleneglycol monoethyl ether, ethylene glycol monobutyl ether, diethyleneglycol monomethyl ether, diethylene glycol monobutyl ether, propyleneglycol monomethyl ether, propylene glycol monobutyl ether, dipropyleneglycol monomethyl ether, triethylene glycol monomethyl ether, ethyleneglycol diacetate, ethylene glycol monomethyl ether acetate, triethyleneglycol monomethyl ether, triethylene glycol monoethyl ether or ethyleneglycol monophenyl ether); an amine (for example, triethylenetetramine,polyethyleneimine or tetramethylpropylenediamine); an amide; and otherorganic solvents such as, for example, dimethylsulfoxide, sulfolane,2-pyrrolidone, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone,2-oxazolidone, or 1,3-dimethyl-2-imidizolidinone). The above-mentionedorganic solvents can be used in combination of two or more thereof. Insome examples in accordance with the principles described herein, theorganic solvent is an acetate, a glycol, a glycol ether or aheterocyclic ketone, or a combination of two or more of the above.

In some examples in accordance with the principles described herein, theamount of organic solvent in the dispersing agent is about 30% to about50%, or about 30% to about 45%, or about 30% to about 40%, or about 30%to about 35%, or about 35% to about 50%, or about 35% to about 45%, orabout 35% to about 30%, or about 35% to about 50%, or about 35% to about45%, or about 35% to about 40%, by weight of the dispersing agent, forexample.

Some examples of particular organic solvents that may be in thedispersing agent in accordance with the principles described hereininclude, by way of illustration and not limitation, acetates such as,e.g., methoxypropylacetate and butyl acetate, and glycols such as, forexample, butylglycol, for example.

In some examples in accordance with the principles described herein, thedispersing agent may further comprise a (meth)acrylic monomer in placeof some or all of the aforementioned organic solvent. The use of(meth)acrylic monomer in place of some or all of the organic solvent mayresult in better curing properties or ink stability depending on thecomposition of an ink composition. The phrase “(meth)acrylic monomer”includes both acrylic monomers and methacrylic monomers. In someexamples, the (meth)acrylic monomer is selected from the groupconsisting of 2-phenoxyethyl acrylate, isophoryl acrylate, isodecylacrylate, tridecyl acrylate, lauryl acrylate, 2-(2-ethoxy-ethoxy)ethylacrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, propoxylatedacrylate, tetrahydrofurfuryl methacrylate, 2-phenoxyethyl methacrylate,and isobornyl methacrylate, and combinations of two or more of theabove.

In some examples in accordance with the principles described herein, thetotal amount of (meth)acrylic monomer and organic solvent in thedispersing agent is about 30% to about 50%, or about 30% to about 45%,or about 30% to about 40%, or about 30% to about 35%, or about 35% toabout 50%, or about 35% to about 45%, or about 35% to about 40%, byweight of the dispersing agent, for example. In some examples inaccordance with the principles described herein, one or both of theorganic solvent and the (meth)acrylic monomer may be provided in acommercially available dispersing agent.

The mill base composition in accordance with the principles describedherein includes a pigment, which in many examples is a particulatepigment. The particulate pigment may be inorganic or organic. In someexamples, the pigment of the ink composition is a pigment coated with orencapsulated in an organic polymer. The pigment may be anaturally-occurring pigment or a synthetic pigment. The pigment can beof any color including, but not limited to, black, blue, brown, cyan,green, white, violet, magenta, red, orange and yellow, as well as spotcolors from mixtures thereof.

The particulate pigment may be a single particulate pigment or a mixtureof two or more particulate pigments. Thus, there may be at least oneparticulate pigment or at least two particulate pigments or at leastthree particulate pigments, for example. The number of pigments in amixture of pigments that comprise the particulate pigment is in therange of 2 to about 5, or 2 to about 4, or 2 to about 3. The particulatepigment for the mill base composition is in many instances in the formof larger particles having an average diameter of about 1 micron toabout 500 microns, or about 10 micron to about 500 microns, or about 100micron to about 500 microns, or about 1 micron to about 400 microns, orabout 1 micron to about 300 microns, or about 1 micron to about 200microns, or about 1 micron to about 100 microns, for example.

The shape of the particulate pigment may be regular or irregular. Theparticulate pigment may be in the form of a bead, flake, plate, rod,platelet, cube and column, for example. In some examples thecross-sectional shape of the particulate pigment may be circular,triangular, square, quadrangular, hexangular, oval, scalloped,corrugated, or ellipsoidal, for example.

Examples of organic pigments that may be present in the ink compositioninclude, by way of illustration and not limitation, perylenes,phthalocyanine pigments (for example, phthalo green, phthalo blue),cyanine pigments (Cy3, Cy5, and Cy7), naphthalocyanine pigments, nitrosopigments, monoazo pigments, diazo pigments, diazo condensation pigments,basic dye pigments, alkali blue pigments, blue lake pigments, phloxinpigments, quinacridone pigments, lake pigments of acid yellow 1 and 3,isoindolinone pigments, dioxazine pigments, carbazole dioxazine violetpigments, alizarine lake pigments, vat pigments, phthaloxy aminepigments, carmine lake pigments, tetrachloroisoindolinone pigments,perinone pigments, thioindigo pigments, anthraquinone pigments andquinophthalone pigments, for example, and mixtures of two or more of theabove and derivatives of the above.

Inorganic pigments that may be present in the pigment dispersion,include, for example, metal oxides (for example, titanium dioxide,electrically conductive titanium dioxide, iron oxides (e.g., red ironoxide, yellow iron oxide, black iron oxide and transparent iron oxides),aluminum oxides, silicon oxides), carbon black pigments (e.g., furnaceblacks), metal sulfides, metal chlorides, and mixtures of two or morethereof.

Particular examples of pigment colorants that may be employed include,by way of illustration and not limitation, yellow pigments having thefollowing Yellow Pigment color index PY 83, PY 151, PY 150, PY 155, PY139, PY120, PY180, PY 129 and PY 154, PY 213. Magenta pigments composedof Red pigment having color indices of PR 202, PR 254, PR 122, PR 149,PR 185, PR 255, PR 146 and Violet pigment having color indices of PV 19,PV 23, PV 37 and PV 29 may be used. Blue pigments having color indicesof PB 15:3, PB 15:4, PB 15:2, and PB 15:1, as well as black pigmentshaving color indices of PBL Black 7 may be utilized. Inorganic pigmentsuch as a white pigment of the type TiO₂ may be used. Orange pigmenthaving color indices of PO46, PO64, PO34 as well as green pigmentshaving color index of PG7 may be employed.

Certain pigments that may be employed in examples in accordance with thepresent disclosure are found under the trade names PALIOTOL®, HELIOGEN®,CHROMOPHTAL®, IRGALITE®, and CINQUASIA® (available from BASFCorporation, Port Arthur Tex.), HOSTAPERM® and NOVOPERM® (available fromClariant International Ltd., Muttenz, Switzerland), SUNFAST® and QUINDO®(available from SunChemical Corporation, Riverside Calif.), SPECIALBLACK® (available from Evonik Degussa Corporation, Theodore Ala.),KRONOS® (Kronos Inc., Cranbury N.J.), and KEMIRA® (Kemira ChemicalsInc., Atlanta Ga.).

The amount of the pigment in the mill base composition depends on anumber of factors, for example, the nature of the pigment, the nature ofthe dispersing agent, the nature of the use of an ink compositioncomprising the milled mill base composition, and the nature of anyadditives, for example. The mill base composition may contain an amountof pigment (percent by weight of the mill base composition) of about 10%to about 70%, or about 10% to about 60%, or about 10% to about 50%, orabout 10% to about 40%, or about 10% to about 30%, or about 10% to about20%, or about 20% to about 70%, or about 20% to about 60%, or about 20%to about 50%, or about 20% to about 40%, or about 20% to about 30%, orabout 30% to about 70%, or about 30% to about 60%, or about 30% to about50%, or about 30% to about 40%, or about 40% to about 70%, or about 40%to about 60%, or about 40% to about 50%, for example. The amount ofpigment present in the mill base composition may range between anycombinations of these values, inclusive of the recited values.

In some examples in accordance with the principles described herein, themill base composition may comprise other components to improveproperties or performance of the mill base composition, for example.Such components include, but are not limited to, one or more ofanti-foaming agents, polymerization stabilizers, and synergists, forexample. The total amount by weight of such components in the mill basecomposition is about 0.1% to about 1%, or about 0.1% to about 0.5%, orabout 0.1% to about 0.2%, or about 0.2% to about 1%, or about 0.2% toabout 0.5%, or about 0.5% to about 1%, for example.

Specific examples of polymerization stabilizers, by way of illustrationand not limitation, include GENORAD® 16 (Rahn USA Corporation, AuroraIll.), IRGASTAB® UV22 (BASF), for example. Specific examples ofsynergists, by way of illustration and not limitation, includeSOLSPERSE® 5000, SOLSPERSE® 22000 (both from Lubrizol), for example.Specific examples of anti-foaming agents that are commercially availableinclude, but are not limited to, FOAMEX® 800, FOAMEX® 805, FOAMEX® 845,FOAMEX® 842, and FOAMEX® 835 (all available from Evonik Tego ChemieService GmbH, Essen, Germany) and TWIN® 4000 (Evonik Tego Chemie ServiceGmbH); and BYK® 019, BYK® 028, and BYK® 029 (available from BYK ChemieGmbH, Wesel, Germany), for example.

Mill base compositions in accordance with the principles describedherein, after milling, may be employed in ink compositions, which inmany examples are curable by UV application. The mill base compositionis subjected to milling and then combined with an ink vehicle to producean ink composition.

Milling may be carried out using a horizontal bead mill, a vertical beadmill, or a basket mill, for example. In some examples, a horizontal beadmill is employed. In the milling step, a mill base composition inaccordance with the principles described herein is combined with millingbeads and subjected to conditions to sufficiently mill the mill basecomposition to such that larger pigment particles are broken intopigment particles of a size suitable for ink compositions. The resultingpigment particles are stabilized by the dispersing agent.

The composition of the milling beads employed should be such that themilling beads exhibit good fracture resistance and abrasion resistance,for example. The composition of the milling beads may be, by way ofillustration and not limitation, glass, a metal oxide, or a metal alloy,for example. Metal oxides suitable as milling beads include, but are notlimited to, zirconium oxide, for example.

The diameter of the milling beads depends on one or more of the natureof the milling beads and the nature of the pigment particles, forexample. The diameter of the milling beads may be, by way ofillustration and not limitation, about 0.05 mm to about 0.80 mm, orabout 0.05 mm to about 0.65 mm, or about 0.05 mm to about 0.50 mm, orabout 0.05 mm to about 0.35 mm, or about 0.05 mm to about 0.20 mm, orabout 0.10 mm to about 0.80 mm, or about 0.10 mm to about 0.60 mm, orabout 0.10 mm to about 0.40 mm, or about 0.10 mm to about 0.20 mm, orabout 0.20 mm to about 0.80 mm, or about 0.20 mm to about 0.60 mm, orabout 0.20 mm to about 0.40 mm, for example.

In some examples in accordance with the principles described herein, themilling of the mill base composition is carried out in multiple stepssuch as, for example, two steps, three steps, four steps or more withmilling beads of decreasing diameter. In some examples, milling iscarried out in a first step of the milling process with beads that arelarger than about 0.40 mm, or larger than about 0.45 mm, or larger thanabout 0.50 mm, or larger than about, 0.55 mm, or larger than about 0.60mm in diameter or a diameter in the range of about 0.40 mm to about 0.65mm, for example. In a second step of the milling process, the milling iscarried out with beads that are no larger than about 0.30 mm, or nolarger than about 0.25 mm, or no larger than about 0.20 mm, or no largerthan about 0.15 mm, or no larger than about 0.10, or no larger thanabout 0.05 mm in diameter, for example. Additional milling steps may becarried out with beads having a diameter that is progressively lowerthat in the previous steps. In some examples in accordance with theprinciples described herein, a first step of the milling process iscarried out using milling beads having a diameter of about 0.65 mm and asecond step of the milling process is carried out using milling beadshaving a diameter of about 0.1 mm. The step-wise milling process may becarried out using milling beads that are the same composition for eachmilling step or using milling beads in one milling step that have adifferent composition than those of another milling step.

The milling process is carried out for a period of time such that thepigment particles are reduced to a size suitable for use in an inkcomposition. The period of time for the milling process depends on oneor more of the nature of the pigment particles, the nature of themilling beads, and the nature of the milling apparatus, for example. Insome examples the period of time for the each milling step of astep-wise milling process may be the same and in some examples theperiod of time may be different for one or more of the milling steps.The entire milling process may be carried out in about 0.5 hours toabout 8 hours, or about 0.5 hours to about 4 hours, or about 1 hour toabout 2 hours, for example. In a step-wise milling process, duration ofeach step may be, e.g., about 15 minutes to about 3 hours, or about 0.5hours to about 2 hours.

The particle size (cross-sectional dimension) of the pigment in the millbase composition after being subjected to a milling process is in arange from about 1 nanometer (nm) to about 500 nm, or from about 1 nm toabout 400 nm, or from about 1 nm to about 300 nm, or from about 1 nm toabout 200 nm, or from about 1 nm to about 100 nm, or from about 1 nm toabout 50 nm, or from about 5 nm to about 500 nm, or from about 5 nm toabout 400 nm, or from about 5 nm to about 300 nm, or from about 5 nm toabout 200 nm, or from about 5 nm to about 100 nm, or from about 5 nm toabout 50 nm, or from about 10 nm to about 500 nm, or from about 10 nm toabout 400 nm, or from about 10 nm to about 300 nm, or from about 10 nmto about 200 nm, or from about 10 nm to about 100 nm, or from about 10nm to about 50 nm, for example.

The mill base composition after milling functions as a pigmentconcentrate and comprises the milled pigment. The milled mill basecomposition is combined with an ink vehicle to form an ink composition.In some examples in accordance with the principles described herein, aUV curable ink composition comprises the pigment concentrate, one ormore UV curable monomers, and one or more UV initiators. As used herein,“ink vehicle” is defined to include any liquid composition that is usedto carry pigments to an ink-receiving material or substrate. A widevariety of liquid vehicle components may be used. In some examples theliquid vehicle may include, by way of illustration and not limitation,one or more of a variety of different agents, such as one or more of UVcurable agents, UV stabilizers and UV initiators, for example.

The term “UV curable agent” refers to a compound that comprises afunctionality that, when subjected to UV energy, undergoes one or moreof polymerization and crosslinking reactions. Such functionality may becurable by cationic, radical or cationic-radical hybrid mechanisms.Representative examples of UV curable functionalities include, but arenot limited to, (meth)acrylate groups, olefinic carbon-carbon doublebonds, epoxy groups, allyloxy groups, alpha-methyl styrene groups,(meth)acrylamide groups, cyanate ester groups, and vinyl ethers groups,for example, and combinations of two or more of the above.

UV curable agents include, by way of illustration and not limitation, UVradical curable monomers such as, but not limited to, monofunctional(meth)acrylates and multifunctional (di-, tri-, for example)(meth)acrylates, and mono functional and multi functional oligomers, forexample, or combinations of two or more of the above; UV cationiccurable monomers such as, but not limited to, epoxy monomers andoligomers, vinyl ether monomers and oligomers and combinations of two ormore thereof; and UV cationic-radical hybrid monomers, for example.Selection of the appropriate combination of the above agents may be madeon the basis of their ability to impart to an ink composition one ormore of a particular viscosity, film-forming properties, flexibility,adhesion to substrates such as, e.g., plastics, wetting properties,cross-linking density, chemical resistance and scratch resistance ofprinted films, for example.

The curable agent is present in an ink composition in an amount (byweight of the ink composition) of about 10% to about 90%, or about 10 toabout 80%, or about 10% to about 70%, or about 10% to about 60%, orabout 10% to about 50%, or about 10% to about 40%, or about 10% to about30%, or about 20% to about 90%, or about 20 to about 80%, or about 20%to about 70%, or about 20% to about 60%, or about 20% to about 50%, orabout 20% to about 40%, or about 20% to about 30%, or about 30% to about90%, or about 30 to about 80%, or about 30% to about 70%, or about 30%to about 60%, or about 30% to about 50%, or about 30% to about 40%, orabout 40% to about 90%, or about 40 to about 80%, or about 40% to about70%, or about 40% to about 60%, or about 40% to about 50%, for example.

UV agents curable by UV-initiated radical mechanism include, but are notlimited to, 1,6-hexanediol diacrylate (HDDA) (SR238), difunctionalacrylate monomer (SR4423), dipropylene glycol diacrylate (DPGDA)(SR508), tripropylene glycol diacrylate (TPGDA) (SR306), propoxylated2-neopentyl glycol diacrylate (PONPGDA) (SR 9003), tridecyl acrylate(TA) (SR489), isodecyl acrylate (IDA) (SR395), 2-phenoxyethyl acrylate(PEA) (SR339C), lauryl acrylate (LA) (SR335), 2-(2-ethoxyethoxy) ethylacrylate (EOEOEA) (SR256), tetrahydrofurfuryl acrylate (THFA) (SR285),isobornyl acrylate (IBOA) (SR506D), tetrahydrofurfurylmethacrylate(THFMA) (SR203), 2-phenoxyethyl methacrylate (PEMA) (SR 340), isobornylmethacrylate (IBOMA) (SR423), polyester acrylate (ACTILANE® 505, CN2505), dipentaerythritol hexaacrylate (DPHA) (ACTILANE® 450), stearylacrylate (SR257, CD 586D), isooctyl acrylate (SR440), isotridecylacrylate (SR489D), 1,3-butylene glycol diacrylate (SR212),1,4-butanediol diacrylate (SR213), ethoxylated (3) bisphenol Adiacrylate (SR349), tris(2-hydroxyethyl) isocyanurate triacrylate(SR368), trimethylolpropane triacrylate (SR351), polyethylene glycol(200) diacrylate (SR259), tetraethylene glycol diacrylate (SR268),triethylene glycol diacrylate (SR272), tripropylene glycol diacrylate(SR306), polyethylene glycol (400) diacrylate (SR344), ethoxylatedbisphenol A diacrylate (CD9038), pentaerythritol tetraacrylate (SR295),di-trimethylolpropane tetraacrylate (SR355), dipentaerythritolpentaacrylate (SR399), ethoxylated trimethylolpropane triacrylate(SR415), pentaerythritol triacrylate (SR444), ethoxylatedtrimethylolpropane triacrylate (SR454), propoxylated trimethylolpropanetriacrylate (SR492), ethoxylated trimethylolpropane triacrylate (SR499),propoxylated trimethylolpropane triacrylate (SR501), ethoxylatedtrimethylolpropane triacrylate (SR502), propoxylated (3) glyceryltriacrylate (SR9020), propoxylated glyceryl triacrylate (SR9021),ethoxylated trimethylolpropane triacrylate (SR9035, CN435), andethoxylated (4) pentaerythritol tetraacrylate (SR494), for example, andcombinations of two or more above. SR-designated and CD-designatedcurable agents are available from Sartomer USA LLC; ACTILANE®-designatedcurable agents are available from Akzo Nobel Chemicals, Pasadena Calif.

UV agents curable by UV-initiated cationic mechanism include, but arenot limited to, epoxy monomers having 1 to about 6, or 1 to about 3epoxy groups such as, for example, cycloaliphatic mono-epoxides,cycloaliphatic di-epoxides, epoxy grafted polyesters, and oxetanes, forexample. Particular examples of UV agents curable by UV-initiatedcationic mechanism include, but are not limited to, propylene oxide,styrene oxide, vinylcyclohexene oxide, vinylcyclohexene dioxide,glycidol, butadiene oxide, diglycidyl ether of bisphenol A, oxetane,octylene oxide, phenyl glycidyl ether, 1,2-butane oxide,cyclohexeneoxide, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate,dicyclopentadiene dioxide, epoxidized polybutadiene, 1,4-butanedioldiglycidyl ether, polyglycidyl ether of phenolformaldehyde, resorcinoldiglycidyl ether, epoxy silicones (e.g., dimethylsiloxanes havingcycloaliphatic epoxide or glycidyl ether groups), aliphatic epoxymodified with propylene glycol and dipentene dioxide, limonene dioxide,silicone epoxy oligomers, α-pinene oxide, bisphenol-A epoxy,bis(3,4-epoxycyclohexyl)adipate,3,4-epoxycyclo-hexylmethyl-3,4-epoxycyclohexane carboxylate,trimethylolpropane oxetane, and bis{[1-ethyl(3-oxetanyl)]methyl}etheroxetane monomer, for example, and combinations of two or more of theabove.

The presence of organic solvents in an ink composition is primarily theresult of the presence of organic solvent in the mill base compositionor pigment concentrate, which may any of the organic solvents referredto above. In addition, the ink composition may comprise a high molecularweight silicone-based wetting agent such as, for example, TEGO RAD®2100, TEGO RAD® 2200, TEGO RAD® 2250, and TEGO RAD® 2300 (Evonik TegoChemie Service GmbH), and BYK® 307 and BYK® 333 (BYK Chemie GmbH).

The UV initiator or photoinitiator is an agent that initiates a reactionupon exposure to a desired wavelength of UV light to cure an inkcomposition in accordance with the principles described herein afterapplication of the ink composition to an ink-receiving material orsubstrate. The UV initiator may be, by way of illustration and notlimitation, radical, cationic, and radical-cationic, for example. The UVinitiator may be a single compound or a mixture of two or morecompounds. In some examples in accordance with the principles describedherein, a UV initiator is present in the ink composition in an amountsufficient to cure the applied ink composition while maintaining reducedsmear resistance, for example. In some examples, the UV initiator ispresent in the ink composition in an amount of from about 0.01% to about10%, or about 1% to about 10%, or about 1% to about 5%, or about 1% toabout 2% by weight, based on the total weight of the ink composition.

Examples of cationic UV initiators include, by way of illustration andnot limitation, aryldiazonium salts, diaryliodonium salts,triarylsulphonium salts, triarylselenonium salts,dialkylphenacylsulphonium salts, aryloxydiarylsulphoxonium salts, anddiarylphenacylsulphoxonium salts, for example. Particular examples ofcationic UV initiators include, but are not limited to,diphenyl(4-phenylthio)-phenylsulfonium hexafloroatimonate,(thiodi-4,1-phenylene)bis(diphenylsulfonium)dihexafluoroatimonate (amixture of the two sold under the name CHIVACURE® 1176 from ChitecTechnology Co. Ltd, Phoenix Ariz.),diphenyl(4-phenylthio)-phenylsulfonium hexafluorophosphate,(thiodi-4,1-phenylene)bis(diphenylsulfonium)dihexafluorophosphate (amixture of the two sold under the name CHIVACURE® 1190 from ChitecTechnology Co. Ltd), triarylsulphonium hexafluorophosphate salt(CYRACURE® UVI-6990) and triarylsulphonium hexafluoroantimonate salt(CYRACURE® UVI-6974) (both available from Union Carbide Chemicals andPlastics Co. Inc., Danbury, Conn.), triphenylselenoniumhexafluoroantimonate, triphenylsulfonium hexafluoroantimonate,triphenylsulfonium hexafluorophosphate, bis(4-dodecylphenyl)-iodoniumhexafluoroantimonate, and η-5-2,4-cyclopentadiene-1-yl)[(1,2,3,4,5,6-η)-(1-methylethyl)benzene] iron (1+) hexafluorophosphate(1−) (IGRACURE® 261 from Ciba-Geigy Corporation, McIntosh Ala.), forexample, and combinations or two or more of the above.

Examples of radical UV initiators include, by way of illustration andnot limitation, 1-hydroxy-cyclohexylphenylketone, benzophenone,2,4,6-trimethylbenzo-phenone, 4-methylbenzophenone, 2-benzyl2-dimethylamino 1-(4-morpholinophenyl)butanone-1,2-methyl-1-(4-methylthio)phenyl-2-(4-morpholinyl)-1-propanone,diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide,2,4,6-trimethylbenzoylphenylphosphinic acid ethyl ester,oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone),2-hydroxy-2-methyl-1-phenyl-1-propanone, benzyl-dimethyl ketal,isopropylthioxanthone. Amine synergists may also be used, for examplesuch as ethyl-4-dimethylaminobenzoate, 2-ethylhexyl-4-dimethylaminobenzoate, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one(OMNIRAD® 4817 from IGM Resins, Bartlett Ill.),2,4,6-trimethylbenzoyl-diphenyl phosphine oxide (OMNIRAD® TPO from IGMResins), 2-isopropylthioxanthone (OMNIRAD® ITX from IGM Resins), andbis(2,4,6-trimethylbenzoyl)-phenylphosphine-oxide (IRGACURE® 819 fromBASF Corporation), for example, and combinations of two or more of theabove.

As mentioned above, the ink compositions may comprise a UV stabilizer,that is, an agent that can assist with scavenging free radicals.Examples of UV stabilizers include, by way of illustration and notlimitation, quinine methide (IRGASTAB® UV 22 from BASF Corporation) andGENORAD® 16 (Rahn USA Corporation), for example, and combinations of twoor more UV stabilizers.

The amount of milled mill base composition or pigment concentrate in theink composition depends on a number of factors, for example, the natureof the pigment, the nature of the mill base composition, the nature ofthe use of the ink composition, the nature of the jetting mechanism forthe ink, and the nature of additives. In some examples, the amount(percent by weight) of pigment concentrate in the ink composition isabout 0.1% to about 20%, or about 0.1% to about 15%, or about 0.1% toabout 10%, or about 0.1% to about 5%, or about 0.5% to about 20%, orabout 0.5% to about 15%, or about 0.5% to about 10%, or about 0.5% toabout 5%, or about 1% to about 20%, or about 1% to about 15%, or about1% to about 10%, or about 1% to about 5%, or about 2% to about 20%, orabout 2% to about 15%, or about 2% to about 10%, or about 2% to about5%, or about 3% to about 20%, or about 3% to about 15%, or about 3% toabout 10%, or about 3% to about 5%, for example.

The milled mill base composition and the ink vehicle are combined underconditions such that the pigment becomes substantially evenly dispersedin the ink vehicle. In some examples, the combination is agitated for aperiod of about 10 to about 100 minutes, or about 10 to about 80minutes, or about 10 to about 60 minutes, or about 10 to about 40minutes, or about 20 to about 100 minutes, or about 20 to about 80minutes, or about 20 to about 60 minutes, or about 20 to about 40minutes, or about 25 to about 50 minutes, or about 25 to about 35minutes, for example. Agitation may be accomplished, for example, bysonication, ultrasonication, or microfluidization, or a combination ofthe above. The temperature during formation of the dispersion may beabout 10° C. to about 40° C., or about 10° C. to about 35° C., or about10° C. to about 30° C., or about 10° C. to about 25° C., or about 10° C.to about 20° C., or about 15° C. to about 30° C., or about 15° C. toabout 25° C., or about 15° C. to about 20° C., for example.

The ink composition may be filtered to remove large particles that areoutside the range of those for use in an ink composition because, forexample, the larger particles may prohibit or reduce the reliability ofthe jetting of the ink composition. In some examples, the inkcomposition is subjected to filtration using a filtration device havingpores of a size that excludes such larger particles. Filtration may becarried out using, by way of illustration and not limitation, one ormore of membrane filtration, surface filtration, depth filtration,screen filtration, and filtration aid, for example.

In some examples in accordance with the principles described herein, theink compositions find use as inkjet inks for inkjet printers. In someexamples the ink compositions may be dispensed to the surface of a broadrange of substrates employing inkjet technology and equipment. Thesubstrate may be planar, either smooth or rough, or such other shapethat is suitable for the particular purpose for which it is employed.The substrate may be porous or non-porous, rigid, semi-rigid, orflexible, for example. Planar substrates may be in the form, forexample, of a film, plate, board, or sheet by way of illustration andnot limitation. Examples of substrate materials include, but are notlimited to, plastic substrates (for example, cellulose diacetate,cellulose triacetate, cellulose propionate, cellulose butyrate,cellulose acetate butyrate, nitrocellulose, polyethylene terephthalate,polyethylene, polystyrene, polypropylene, polycarbonate, polyvinylacetal, and acrylic), paper, paper laminated with plastic (for example,polyethylene, polypropylene, or polystyrene), cardboard, paperboard,foam board, and textiles.

In some examples in accordance with the principles described herein, thesubstrate has a thickness of about 0.1 mm to about 10 mm, or about 0.1mm to about 5 mm, or about 0.1 mm to about 1 mm, or about 0.1 mm toabout 0.6 mm, or about 0.5 mm to about 10 mm, or about 0.5 mm to about 5mm, or about 0.5 mm to about 1 mm, or about 0.5 mm to about 0.6 mm, orabout 1 mm to about 10 mm, or about 1 mm to about 5 mm, or about 1 mm toabout 2 mm, for example.

Examples of ink compositions in accordance with the principles describedherein may be dispensed from any piezoelectric, drop-on-demand inkjetprinting device and many such devices are commercially available. Suchinkjet printing devices are available from Hewlett-Packard, Inc., PaloAlto, Calif., by way of illustration and not limitation. In inkjetprinting devices for inkjet printing, liquid ink drops are applied in acontrolled fashion to an ink-receiving substrate by ejecting inkdroplets from a plurality of nozzles, or orifices, in a print head of aninkjet printing device or inkjet printer. In drop-on-demand systems, adroplet of ink is ejected from an orifice directly to a position on thesurface of an ink receiving substrate by pressure created by, forexample, a piezoelectric device, an acoustic device, or a thermalprocess controlled in accordance digital data signals. An ink droplet isnot generated and ejected through the orifices of the print head unlessit is needed. The volume of the ejected ink drop is controlled mainlywith a print head.

The printed or jetted ink on the substrate may be subjected to suitablelight sources for curing the ink compositions in accordance with theprinciples described herein. The type of light source depends on, forexample, the UV initiator used. In some examples, UV initiators can beactivated by high pressure mercury lamps, xenon-lamps, arc lamps andgallium lamps, for example.

In some examples, a photosensitizer may be used with the UV initiator inamounts of about 0.01% to about 10%, or about 0.01% to about 5%, orabout 0.01% to about 3%, or about 0.01% to about 1%, or about 0.1% toabout 10%, or about 0.1% to about 5%, or about 0.1% to about 3%, orabout 0.1% to about 1%, or about 1% to about 10%, or about 1% to about5%, or about 1% to about 3%, or about 1% to about 2%, by weight, basedon the total weight of the ink composition. A photosensitizer absorbsenergy and then transfers it to another molecule, usually thephotoinitiator. The structure of the photosensitizer remains unchanged.Photosensitizers are often added to shift the light absorptioncharacteristics of a system. An example of a photosensitizer isanthracene, which is used with the diphenyliodonium cation. Suitableexamples of photosensitizers include, but are not limited to,anthracene, perylene, phenothiazine, xanthone, thioxanthone, andbenzophenone, for example. A photopolymerization initiation promoter mayalso be used. This is an agent which is not activated itself byultraviolet radiation but which, when used with a photopolymerizationinitiator, helps the initiator speedup the initiation of polymerization;thus, realizing a more efficient cure.

DEFINITIONS

The following provides definitions for terms and phrases used above,which were not previously defined.

The phrase “at least” as used herein means that the number of specifieditems may be equal to or greater than the number recited. The phrase“about” as used herein means that the number recited may differ by plusor minus 10%; for example, “about 5” means a range of 4.5 to 5.5. Theterm “between” when used in conjunction with two numbers such as, forexample, “between about 2 and about 50” includes both of the numbersrecited as well as all of the numbers within the range and fractions ofall of the numbers between and including 2 to 50. Any ranges of valuesprovided herein include values and ranges within or between the providedranges. As used herein, the singular forms “a”, “an” and “the” includeplural referents unless the content clearly dictates otherwise. In someinstances, “a” or “an” as used herein means “at least one” or “one ormore.” Designations such as “first” and “second” are used solely for thepurpose of differentiating between two items and are not meant to implyany sequence or order or importance to one item over another or anyorder of operation, for example.

The term “substituted” means that a hydrogen atom of a compound ormoiety is replaced by another atom such as a carbon atom or aheteroatom, which is part of a group referred to as a substituent.Substituents include, for example, alkyl, alkoxy, aryl, aryloxy,alkenyl, alkenoxy, alkynyl, alkynoxy, thioalkyl, thioalkenyl,thioalkynyl, and thioaryl.

The term “heteroatom” as used herein means nitrogen, oxygen, phosphorusor sulfur. The term “heterocyclic” means having an alicyclic or aromaticring structure, which includes one or more heteroatoms.

EXAMPLES

Unless otherwise indicated, materials in the experiments below may bepurchased from Aldrich Chemical Company, St. Louis Mo. Parts andpercentages are by weight unless indicated otherwise.

The following abbreviations were used in the discussion below:

Abbreviation Definition min minute(s) % wt percentage by weight m/smeters per second l/s liter per second d₅₀ (Zave) mean particle size cpcentipoise PI Photoinitiator nm nanometer ml milliliter

The following materials were employed in the examples below:

Material Chemical Name Manufacturer/Supplier AVES divinyl ester ofadipic acid BASF Corporation SOLSPERSE ® J200 Lubrizol Corporation(dispersing agent) 228-6742 magenta pigment Sun Chemical Corp., (PV19)Riverside CA CN435 (acrylic monomer) ethoxylated trimethylol-propaneSartomer USA LLC, triacrylate Exton PA SR-9003 (acrylic monomer)propoxylated neopentyl glycol Sartomer diacrylate SR-285 (acrylicmonomer) tetrahydrofurfuryl acrylate Sartomer Vinylcaprolactam (mono-ISP Investments Inc., functional curable monomer) Wilmington DE AGISYN ®670A2 aromatic urethane acrylate AGI Corporation, Taipei (acrylicmonomer) Taiwan OMNIRAD ® 4817 2-methyl-1-[4-(methylthio)phenyl]- IGMResins, Bartlett IL (radical PI) 2-morpholinopropan-1-one OMNIRAD ® TPO2,4,6-trimethylbenzoyl-diphenyl IGM Resins (radical PI) phosphine oxideOMNIRAD ® ITX (radical PI) 2-isopropylthioxanthone IGM Resins IRGASTAB ®UV 22 quinone methide BASF Corporation (UV stabilizer) BYK ® 333(surfactant) a polyether modified BYK Chemie GmbH dimethylpolysiloxaneBYK ®-LP N 21421 BYK Chemie GmbH (dispersing agent) IRGALITE ® Blue GLVOBASF Corporation (pigment) TEGORAD ® 2200 silicone polyether acrylateEvonik Tego Chemie (surfactant) Service GmbH SR506D (acrylic monomer)isobornyl acrylate Sartomer DOUBLEMER ® 4300 cycloaliphatic epoxidemonomer Double Bond Chemical (cationic monomer) Industries USA Inc.,West Simsbury CT TMPO (cationic monomer) trimethylolpropane oxetanePerstorp, Toledo OH OXT 221 (cationic monomer) bis{[1-ethyl(3-oxetanyl)]methyl} Toagosei Co. Ltd, Tokyo ether oxetane monomer Japan SR 399LV(acrylic monomer) dipentaerythritol pentaacrylate Sartomer CHIVACURE ®1176 Mixture of diphenyl(4-phenyl Chitec Technology Co. (cationic PI)thio)-phenylsulfonium hexa Ltd, Phoenix AZ floroatimonate and(thiodi-4,1- phenylene)bis(diphenylsulfonium) dihexafluoroatimonateCHIVACURE ® 1190 Mixture of diphenyl(4- Chitec Technology Co. (cationicPI) phenylthio)-phenylsulfonium Ltd hexafluorophosphate and (thiodi-4,1-phenylene) bis(diphenyl sulfonium) dihexafluorophosphate IRGACURE ®819 bis(2,4,6-trimethylbenzoyl)phenyl BASF Corporation (radical PI)phosphine oxide

The following test procedures were employed in the examples below:

Procedure for Testing Viscosity

The viscosity of the mill base compositions and for inkjet inkcompositions was determined using a HAAKE RS-600 rheometer (ThermoElectron, Newington N.H.) and a TCP/P Peltier controlled unit (ThermoElectron). The viscosity was measured at a temperature of 25° C. forsamples of mill base compositions and 40° C. for samples of inkjet inkcompositions. The results were recorded at two shear rates of 500 1/sand 4000 1/s.

Procedure for Particle Size Testing—d₅₀ (Zave)

The d₅₀ particle size was determined using a Malvern Zetasizer Nano(Malvern Instruments, Malvern, Worcestershire UK). The sample wasdiluted at 1:1000 ratio in pure triethyleneglycol divinyl ether.

Procedure for Testing Curing Speed

The curing speed of samples of the inkjet ink compositions wasdetermined using LC6B bench top conveyer with LH6 UV curing system(Fusion UV systems Inc., Gaithersburg Md.). The ink sample was appliedto self adhesive vinyl by draw down using a K Control Coater (RK PrintCoat Instruments Ltd, Litlington, UK) in a thickness of 12 or 6 microns.The ink was irradiated once under the UV lamp at different conveyerspeeds. The cured ink film was tested by scratching using a paper clipimmediately after each pass. The highest speed at which ink could not bescratched was reported as the curing speed.

Procedure for Testing Optical Density of Inkjet Ink Compositions

Optical density of inkjet ink compositions was tested using Beta Colordensitometer (Beta Industries, Inc., Dayton Ohio). The ink sample wasapplied to self adhesive vinyl by draw down using a K Control Coater (RKPrint Coat Instruments Ltd) in a thickness of 12 microns. The ink samplewas fully cured before testing the optical density.

Procedure for Testing the Stability of Inkjet Ink Compositions

Samples of mill base compositions and inkjet ink compositions samplewere placed in an oven at a temperature of 45° C. Viscosity of the agedsample was tested periodically in accordance with the proceduredescribed above.

Example 1

The example is directed to a mill base composition comprising a divinylester of a dicarboxylic acid as a milling vehicle and inkjet inkcompositions prepared from the milled mill base composition.

A combination of AVES (55%), SOLSPERSE® J200 (dispersing agent, 15%) and228-6742 (magenta pigment, 30%) was prepared. A 200 ml sample of thiscombination was pre-mixed in a high shear mixer for 30 min. Then, thesample was transferred to a horizontal bead mill (Mini 100 millavailable from Eiger Machinery Inc., Grayslake Ill.) for the firstmilling stage, in which 0.65 mm ZiO₂ YTZ beads (ZIRMIL® available fromSaint-Gobain Zirpro, Le Pontet Cedex, FR) were used as the millingbeads. The sample was milled at 3000 rpm for 60 min. The sample wastransferred to a second mill identical to the first one but equipped towork with micro media beads. In the second milling stage the sample wasmilled with 0.1 mm ZiO₂ YTZ beads at 3500 rotations per min (rpm) for 60min. Samples were taken after 15, 30 and 60 min. The mill base had thefollowing composition: AVES (55%), SOLSPERSE® J200 (dispersing agent,15%) and 228-6742 (magenta pigment, 30%). The viscosity and particlesize of the mill base of Example 1 are presented in Table 1.

TABLE 1 Viscosity Viscosity (cp) (cp) Particle Example 1 Mill Base at500 l/s at 4000 l/s Size (nm) 1^(st) stage - 60 min, 0.65 mm beads 10791 175 2^(nd) stage - 15 min, 0.1 mm beads 106 78 179 2^(nd) stage - 30min, 0.1 mm beads 112 83 154 2^(nd) stage - 60 min, 0.1 mm beads 139 95137

An ink composition for an inkjet printer was prepared and had thefollowing components:

Component Name Functionality % wt CN 435 Acrylic monomer 10 SR 9003Acrylic monomer 25 SR 285 Acrylic monomer 15 V-Cap Vinylcaprolactam 20.7AGISYN ® 670A2 Acrylic monomer 10 OMNIRAD ® 4817 Radical PI 1.5OMNIRAD ® TPO Radical PI 3.5 OMNIRAD ® ITX Radical PI 2 IRGASTAB ® UV22UV stabilizer 0.1 BYK ® 333 Surfactant 0.2 Mill base (Example 1) Pigmentconcentrate 12

The above inkjet ink composition was prepared with two samples of themill base composition of Example 1, a first sample with mill basecomposition taken from the second stage after 15 min of milling, thesecond sample with mill base taken from the second stage after 60 min ofmilling. The inkjet ink optical density, viscosity upon assembly andafter 2 weeks of aging in a 45° C. oven is presented in Table 2.

TABLE 2 t = 0 (upon assembly) t = 2 weeks @ 45° C. Viscosity ViscosityViscosity Viscosity Example 1 Optical (cp) at 500 (cp) at 4000 (cp) at500 (cp) at 4000 Inkjet Inks Density 1/s 1/s 1/s 1/s Ink 1 1.84 11.711.46 11.84 11.52 Mill Base 15 min Ink 2 1.85 11.84 11.52 12.6 12.09Mill Base 60 min

The curing speed of the inkjet inks samples was tested according to thetest procedure described above. The maximum curing speed was found to be2 m/s.

Example 1A

For purposes of comparison, a mill base composition was prepared withacrylic monomer as a known milling vehicle in place of AVES of Example 1and an inkjet ink was prepared therefrom. The ink was produced using thesame dispersant, pigment and milling conditions as the ink of Example 1.A combination of SR 9003 (55%), SOLSPERSE® J200 (dispersing agent, 15%)and 228-6742 (magenta pigment, 30%) was prepared and subjected to thesame milling process as described in Example 1. The viscosity andparticle size of the mill base in comparative Example 1A are presentedin Table 3.

TABLE 3 Viscosity Viscosity (cp) (cp) Particle Mill Base - Example 1A at500 1/s at 4000 1/s Size (nm) 1^(st) stage - 60 min, 0.65 mm beads 330280 161 2^(nd) stage - 15 min, 0.1 mm beads 160 137 135 2^(nd) stage -30 min, 0.1 mm beads 184 151 133 2^(nd) stage - 60 min, 0.1 mm beads 230175 119

A test inkjet ink formulation was prepared from the mill base of Example1A in the same manner as in Example 1 with two samples of mill basetaken after 15 min and 60 min, respectively. The other components of theinkjet ink formulation were as set forth above for the inkjet inkformulation produced using the mill base composition of Example 1. Theoptical density and the viscosity upon assembly and after 2 weeks ofaging in a 45° C. oven for the inkjet formulation prepared from the millbase of Example 1A is presented in Table 4 for purposes of comparison.

TABLE 4 t = 0 (upon assembly) t = 2 weeks @ 45° C. Viscosity ViscosityViscosity Viscosity Example 1A Optical (cp) at 500 (cp) at 4000 (cp) at500 (cp) at Inkjet Inks Density 1/s 1/s 1/s 4000 1/s Ink 1 1.88 13.413.2 13.7 13.4 Mill Base 15 min Ink 2 1.84 14.45 14.2 14.8 14.4 MillBase 60 min

Inkjet ink samples of the comparative Example 1A were tested for curingspeed according to the procedure described above. The maximum curingspeed was found to be 2 m/s.

Discussion of Results of Example 1 and Comparative Example 1A

The use of AVES as a milling vehicle produced a mill base compositionwith considerably lower mill base viscosity than that for a mill basecomposition where a known milling vehicle, namely, an acrylic monomer(SR 9003) was employed. The mill base viscosity with AVES was under 100cp in 4000 1/s as compared to 150 cp in 4000 1/s for the mill base madewith acrylic monomer (SR 9003). The lower viscosity mill base allows forbetter usage in inkjet ink formulations achieving lower viscosity inksThe inkjet ink of Example 1 was 1.94 cp and 2.68 cp lower at 4000 1/s(15 min and 60 min, respectively) compared to the inkjet ink incomparative Example 1A. Milling with AVES in the mill base compositionallowed for better rheology control in the inkjet ink prepared therefromthan that of comparative Example 1A. It can be seen that inkjet ink madewith a mill base composition comprising AVES and milled for 15 min and60 min resulted in similar viscosities of 11.46 cp and 11.58 cp in 40001/s, respectively, whereas a mill base composition made with acrylicmonomer SR 9003 resulted in different inkjet ink viscosities of 13.4 cpand 14.2 cp in 4000 1/s, respectively.

The particle size of the mill base composition of Example 1 was a littlelarger than that for the mill base composition of comparative Example1A, by 16 nm and 18 nm after 15 min and 60 min, respectively. Thisdifference is not significant and does not influence color density asthere was a negligible difference in optical density measurements madeon the printed articles using the respective inkjet ink samples ofExamples 1 and 1A.

Samples of inkjet ink prepared in Example 1 exhibited aging stability ina 45° C. oven that was comparable to the samples of inkjet ink preparedin Example 1A. The results of the aging stability studies of the inkjetinks prepared in Examples 1 and 1A are summarized in Table 5.

TABLE 5 % Change % Change Inkjet Sample 500 1/s 4000 1/s Mill base ofExample 1 - 15 min 2.24% 1.51% Mill base of Example 1 - 60 min 6.50%5.30% Comparative Example 1A - 15 min 1.20% 0.50% Comparative Example1A - 60 min 6.40% 4.90%

The above ink aging results are considered to be within an acceptablethreshold for inkjet inks The inkjet ink of Example 1 exhibited similarcuring speed as with inkjet ink of comparable Example 1A indicating thatusing AVES in a mill base composition rather than the known acrylicmonomer (SR 9003) milling vehicle did not influence inkjet ink curingspeed.

Example 2

This example was carried out in a manner similar to that for Example 1with the exception that a different dispersant was employed in the millbase composition and the components of the mill base composition werepresent in different weight percentages than that of Example 1. Acombination of AVES (40%), BYK®-LP N 21421 (dispersing agent, 30%) and228-6742 (magenta pigment, 30%) was prepared. The components werepre-mixed in a high shear mixer in the order given and milled using thesame milling conditions described in Example 1. Samples were taken atthe same time intervals. The viscosity and particle size of the millbase composition of Example 2 are summarized in Table 6:

TABLE 6 Viscosity Viscosity Particle (cp) (cp) Size Example 2 Mill Baseat 500 1/s at 4000 1/s (nm) 1st stage - 60 min, 0.65 mm beads 77 57 1762nd stage - 15 min, 0.1 mm beads 68 53 150 2nd stage - 30 min, 0.1 mmbeads 95.5 66.5 140 2nd stage - 60 min, 0.1 mm beads 223 110 136

An inkjet ink formulation was prepared in the same manner as in Example1 with the exception that the above mill base composition of Example 2was employed in place of the mill base composition of Example 1. Theinkjet ink formulation of Example 2 was prepared with two samples, as inExample 1, with mill base samples after 15 min and 60 min. The opticaldensity and the viscosity upon assembly and after 2 weeks of aging in45° C. oven for the inkjet formulation prepared from the mill basecomposition of Example 2 is presented in Table 7.

TABLE 7 t = 0 (upon assembly) t = 2 weeks @ 45° C. Viscosity ViscosityViscosity Viscosity Example 2 Optical (cp) at 500 (cp) at 4000 (cp) at500 (cp) at Inkjet Inks Density 1/s 1/s 1/s 4000 1/s Ink 1 1.82 11.1811.05 12.3 11.96 Mill Base 15 min Ink 2 1.88 11.62 11.45 13.04 12.63Mill Base 60 min

Example 2 inkjet ink samples were tested for curing speed according tothe procedure described above; the maximum curing speed was found to be2 m/s.

Example 2A

For purposes of comparison, a mill base composition was prepared withacrylic monomer as a known milling vehicle in place of AVES of Example 2and an inkjet ink was prepared therefrom. The ink was produced using thesame dispersant, pigment and milling conditions as the ink of Example 2.A combination of SR 9003 (40%), BYK®-LP N 21421 (dispersing agent, 30%)and 228-6742 (magenta pigment, 30%) was prepared and subjected to thesame milling process as described in Example 1. The viscosity andparticle size of the mill base composition in comparative Example 2A arepresented in Table 8.

TABLE 8 Viscosity Viscosity Particle Comparative Example 2A (cp) (cp)Size Mill Base at 500 1/s at 4000 1/s (nm) 1st stage - 60 min, 0.65 mmbeads 196 140 168 2nd stage - 15 min, 0.1 mm beads 189 125 144 2ndstage - 30 min, 0.1 mm beads 362 165 149 2nd stage - 60 min, 0.1 mmbeads 1226 64 144

A test inkjet ink formulation was prepared from the mill base of Example2A in the same manner as in Example 2 with two samples of mill basetaken after 15 min and 60 min, respectively. The other components of theinkjet ink formulation were as set forth above for the inkjet inkformulation produced using the mill base composition of Example 2. Theoptical density and the viscosity upon assembly and after 2 weeks ofaging in a 45° C. oven for the inkjet formulation prepared from the millbase of Example 2A is presented in Table 9 for purposes of comparison.

TABLE 9 t = 0 (upon assembly) t = 2 weeks @ 45° C. Comparative ViscosityViscosity Viscosity Viscosity Example 2A Optical (cp) at 500 (cp) at4000 (cp) at 500 (cp) at Inkjet Inks Density 1/s 1/s 1/s 4000 1/s Ink 11.84 12 11.96 13.86 13.2 Mill Base 15 min Ink 2 1.88 13.2 12.7 16 15.8Mill Base 60 min

Inkjet ink samples prepared from the mill base composition of Example 2Awere tested for curing speed according to the procedure described above;the maximum curing speed was found to be 2 m/s.

Discussion of Results of Example 2 and Comparative Example 2A

As seen in the comparison made in Examples 1 and 1A, using AVES as amilling vehicle resulted in a considerably lower mill base viscositythan the corresponding known milling vehicle, acrylic monomer SR 9003.The viscosity of the mill base composition with AVES was lower than 70cp in 4000 1/s compared to 165 cp in 4000 1/s for the mill basecomposition made with acrylic monomer (SR 9003) up to 30 min millingtime. Milling the mill base composition with AVES (Example 2) up to 60min resulted in a viscosity increase to 223 cp in 500 1/s and 110 cp in4000 1/s whereas milling the mill base composition with acrylic monomerSR9003 (comparative Example 2A) up to 60 min resulted in a viscosityincrease to 1125 cp in 500 1/s and 64 cp in 4000 1/s. The significantdifference in viscosity between low shear and high shear when the millbase composition comprises known acrylic monomer indicates that the millbase composition of Example 2A was not stable under the above millingconditions. Therefore, it appears evident that a mill base compositioncomprising AVES improves product stability during milling.

The lower viscosity mill base composition of Example 2 appeared toprovide better usage in inkjet ink formulations achieving lowerviscosity inks similarly to the data shown in Example 1. The inkjet inkof Example 2 was 0.91 cp to 1.25 cp lower at 4000 1/s (15 min and 60min, respectively) compared to the inkjet ink of comparative Example 2A.

Milling a mill base composition comprising AVES appeared to enablebetter rheology control in an inkjet ink formulation comprising themilled mill base composition comprising AVES. The inkjet ink made withthe mill base composition comprising AVES (Example 2) milled for 15 minand 60 min resulted in viscosities of 11.05 cp and 11.46 cp in 4000 1/s,respectively, bringing the viscosity difference to 0.4 cp, whereas millbase composition comprising acrylic monomer SR 9003 milled for 15 minand 60 min (comparative Example 2A) resulted in inkjet ink viscositiesof 11.96 cp and 12.7 cp in 4000 1/s, respectively, with a viscositydifference of 0.74 cp.

The particle size of the mill base composition of Example 2 wascomparable to the particle size measured in comparative Example 2A inmost milling times, and the difference did not appear to influence colordensity as there was a negligible difference in optical densitymeasurements made on the inkjet inks samples.

Inkjet ink samples of Example 2 showed improved aging stability in a 45°C. oven as compared to the inkjet ink samples of comparative Example 2A.Table 10 summarizes the aging stability of the inkjet inks of Examples 2and 2A.

TABLE 10 % Change % Change Inkjet Sample 500 1/s 4000 1/s Example 2 - 15min 10.00% 8.20% Example 2 - 60 min 12.20% 10.30% Comparative Example2A - 15 min 15.50% 13.90% Comparative Example 2A - 60 min 21.20% 24.40%

Thus, an inkjet ink comprising a milled mill base composition comprisingAVES exhibits improved inkjet ink aging stability. The inkjet ink ofExample 2 exhibited curing speeds similar to that for inkjet ink ofcomparative Example 2A. Thus, it appears that the use of AVES instead ofSR 9003 in a mill base composition did not influence the inkjet inkcuring speed.

Example 3

This example was carried out in a manner similar to that for Example 1with the exception that a different pigment was employed in the millbase composition. A combination of AVES (55%), SOLSPERSE® J200(dispersing agent, 15%) and IRGALITE® Blue GLVO (pigment, 30%) wasprepared. The components were pre-mixed in a high shear mixer in theorder given and milled using the same milling conditions described inExample 1. Samples were taken at the same time intervals. The viscosityand particle size of the mill base composition of Example 3 issummarized in Table 11:

TABLE 11 Viscosity Viscosity Particle (cp) (cp) at Size Example 3 MillBase at 500 1/s 4000 1/s (nm) 1st stage - 60 min, 0.65 mm beads 73.5 64118 2nd stage - 15 min, 0.1 mm beads 85 67.3 198 2nd stage - 30 min, 0.1mm beads 268 111 182 2nd stage - 60 min, 0.1 mm beads 752 231 192

An ink composition for an inkjet printer was prepared and had thefollowing components:

Component Name Functionality % wt CN 435 Acrylic monomer 10 SR 9003Acrylic monomer 25 SR 285 Acrylic monomer 15 V-Cap Vinylcaprolactam 22.7AGISYN ® 670A2 Acrylic monomer 12 OMNIRAD ® 4817 Radical PI 1.5OMNIRAD ® TPO Radical PI 4.5 OMNIRAD ® ITX Radical PI 2 IRGASTAB ® UV22UV stabilizer 0.1 TEGORAD ® 2200 Surfactant 0.2 Mill base (Example 3)Pigment concentrate 7

As in Example 1, the inkjet ink of Example 3 was prepared with twosamples, namely, mill base samples after 15 min and 60 min. The inkjetink optical density, viscosity upon assembly and after 2 weeks of agingin a 45° C. oven is presented in Table 12.

TABLE 12 t = 0 (upon assembly) t = 2 weeks @ 45 C. Viscosity ViscosityViscosity Viscosity Example 3 Optical (cp) at 500 (cp) at (cp) at (cp)at Inkjet Inks Density 1/s 4000 1/s 500 1/s 4000 1/s Ink 1, Mill 2.3911.2 11 11.35 11.05 Base 15 min Ink 2, Mill 2.49 12.17 12 13 12.4 Base60 min

The inkjet inks samples of Example 3 were tested for curing speedaccording to the procedure described above; the maximum curing speed wasfound to be 1.5 m/s.

Example 3A

For purposes of comparison, a mill base composition was prepared withacrylic monomer as a known milling vehicle in place of AVES of Example 3and an inkjet ink was prepared therefrom. The ink was produced using thesame dispersant, pigment and milling conditions as the ink of Example 3.A combination of SR 9003 (55%), SOLSPERSE® J200 (dispersing agent, 15%)and IRGALITE® Blue GLVO (pigment, 30%) was prepared and subjected to thesame milling process as described in Example 3. The viscosity andparticle size of the mill base in comparative Example 3A are presentedin Table 13.

TABLE 13 Viscosity Viscosity Comparative Example 3A (cp) (cp) d₅₀ ZaveMill Base at 500 1/s at 4000 1/s (nm) 1^(st) stage - 60 min, 0.65 mmbeads 221 187 127 2^(nd) stage - 15 min, 0.1 mm beads 229 144 173 2^(nd)stage - 30 min, 0.1 mm beads 415 200 228 2^(nd) stage - 60 min, 0.1 mmbeads 783 290 247

A test inkjet ink formulation was prepared from the mill base of Example3A in the same manner as in Example 3 with two samples of mill basetaken after 15 min and 60 min, respectively. The other components of theinkjet ink formulation were as set forth above for the inkjet inkformulation produced using the mill base composition of Example 3. Theoptical density and the viscosity upon assembly and after 2 weeks ofaging in a 45° C. oven for the inkjet formulation prepared from the millbase of Example 3A is presented in Table 14 for purposes of comparison.

TABLE 14 t = 0 (upon assembly) t = 2 weeks @ 45° C. ComparativeViscosity Viscosity Viscosity Viscosity Example 3A Optical (cp) at 500(cp) at 4000 (cp) at 500 (cp) at Inkjet Inks Density 1/s 1/s 1/s 40001/s Ink 1 2.38 11.96 11.6 12.3 11.9 Mill Base 15 min Ink 2 2.47 12.512.35 13.5 12.63 Mill Base 60 min

Inkjet ink samples prepared from the mill base composition of Example 3Awere tested for curing speed according to the procedure described above;the maximum curing speed was found to be 1.5 m/s.

Discussion of Results of Example 3 and Comparative Example 3A

The improved milling performance of a mill base composition comprisingAVES was observed using a different pigment than that of Example 1. Theviscosity of the mill base composition of Example 3 was up to 111 cp at4000 1/s when milled for 30 min whereas the viscosity of the mill basecomposition of Example 3A was 200 cp at 4000 1/s when milled for 30 min.

A significant difference was noticed in the first stage millingperformance. The viscosity of the mill base composition of Example 3 inthe first stage (after 60 min with 0.65 mm beads) was 73.5 cp and 64 cpat 500 1/s and 4000 1/s, respectively, whereas the viscosity of the millbase composition of Example 3A under the same milling conditions was 221cp and 187 cp at 500 1/s and 4000 1/s, respectively. This largedifference substantiates that the use of AVES in a mill base composition(Example 3) exhibited better performance over a mill base compositioncomprising an acrylic monomer (Example 3A). Furthermore, the mill basecomposition of comparative Example 3A reached a very high viscosityvalue of 415 cp at 500 1/s after 30 min of milling compared to 268 cp atthe same conditions with AVES in the mill base composition of Example 3.In both examples milling to 60 min destabilized the system as can beobserved from the very high viscosity results in 500 1/s.

The lower viscosity of the mill base composition of Example 3 providedfor better usage in inkjet ink formulations achieving lower viscosityinks similarly to the data shown in previous examples. The viscosity ofthe inkjet ink of Example 3 was 0.35 cp to 0.6 cp lower at 4000 1/s (15min and 6 min, respectively) compared to the inkjet ink of comparativeExample 3A.

In both examples measured particle size increased when milling in 0.1 mmbeads compared to 0.65 mm beads. However, in comparative Example 3A theparticle size was significantly larger by 46 nm and 55 nm after 30 minand 60 min of milling, respectively. The data demonstrate that particlesize is increasing with milling time for the mill base composition ofcomparative Example 3A while the particle size remained constant for themill base composition comprising AVES.

Inkjet ink samples of Example 3 showed improved aging stability in a 45°C. oven as compared to the inkjet ink samples of comparative Example 3A.Table 15 summarizes the aging stability of the inkjet inks of Examples 3and 3A.

TABLE 15 % Change % Change Inkjet Sample 500 1/s 4000 1/s Example 3, 15min 1.30% 0.01% Example 3, 60 min 6.82% 3.33% Comparative Example 3A, 15min 2.80% 2.60% Comparative Example 3A, 60 min 8.00% 2.30%

The above aging results are considered to be within acceptable thresholdlevels for inkjet inks The inkjet ink of Example 3 exhibited curingspeeds similar to that for inkjet ink of comparative Example 3A. Thus,it appears that the use of AVES instead of SR 9003 in a mill basecomposition did not influence the inkjet ink curing speed.

Example 4

The milled mill base composition from Example 1 was used to prepare acationic radical hybrid inkjet ink formulation, which had the followingcomponents:

Component Name Functionality % wt SR 506D Acrylic monomer 18 DOUBLEMER ®4300 Cationic monomer 21.65 TMPO Cationic monomer 20 OXT ® 221 Cationicmonomer 14 SR 399LV Acrylic monomer 3 CHIVACURE ® 1176 Cationic PI 2.5CHIVACURE ® 1176 Cationic PI 2.5 IRGACURE ® 819 Radical PI 3.5IRGASTAB ® UV22 UV stabilizer 0.15 TEGORAD ® 2200 Surfactant 0.2 Millbase (Example 1) Pigment concentrate 14.5

The viscosity of the hybrid inkjet ink of Example 4 above was measuredaccording to the procedure described above and was 10.84 cp at 4000 1/s.The stability of the ink was tested and, after two weeks of aging at 45°C., the viscosity of the ink increased to 13.34 cp at 4000 1/s.

Example 4A

The milled mill base composition from Example 1A (wherein an acrylicmonomer SR 90003 was used in the mill base composition in place of AVES)was used to prepare a cationic radical hybrid inkjet ink formulation,which had the same composition as that in Example 4 except for the useof the milled mill base composition of Example 1A in place of the milledmill base composition of Example 1.

The viscosity of hybrid inkjet ink prepared above (Example 4A) wasmeasured according to the procedure described above and was 12.72 cp at4000 1/s. The stability of the ink was tested and, after two weeks ofaging at 45° C., the viscosity of the ink increased to 15.95 cp at 40001/s. In addition, sedimentation and phase separation was observed inhybrid inkjet ink of comparative Example 4A after two weeks of aging at45° C.

Discussion of Results of Example 4 and Comparative Example 4A

The above Examples 4 and 4A demonstrate that a divinyl ester (AVES) canbe used to prepare a mill base composition, which after milling may beemployed advantageously in a cationic radical hybrid ink formulation.The viscosity of the hybrid inkjet ink of Example 4 prepared using amilled mill base composition comprising a divinyl ester component, asmeasured, was 1.88 cp lower than the hybrid inkjet ink prepared using amilled mill base composition comprising an acrylic monomer (SR 9003) asin comparative Example 4A.

The hybrid inkjet ink of Example 4 exhibited increased viscosity aftertwo weeks of aging at 45° C. to 13.34 cp, a significant increase yetstill within working parameters for typical UV inkjet inks, whereas thehybrid inkjet ink of comparative Example 4A exhibited increasedviscosity after two weeks of aging at 45° C. to 15.95 cp, which isconsidered to be a viscosity that is too high for an inkjet ink. Inaddition, the hybrid inkjet ink of comparative Example 4A ink showedphase separation and sedimentation after aging and therefore, the inkjetink of comparative Example 4A is not stable enough to be used in aninkjet application. The hybrid inkjet ink of Example 4 did not exhibitphase separation and sedimentation after aging under the sameconditions.

It should be understood that the above-described examples are merelyillustrative of some of the many specific examples that represent theprinciples described herein. Clearly, those skilled in the art canreadily devise numerous other arrangements without departing from thescope as defined by the following claims.

What is claimed is:
 1. A mill base composition comprising: a compoundcomprising a divinyl ester of a dicarboxylic acid wherein thedicarboxylic acid comprises from 2 to about 8 carbon atoms, a dispersingagent, and a pigment.
 2. The mill base composition according to claim 1wherein the dicarboxylic acid is selected from the group consisting ofoxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid,cyclohexyl dicarboxylic acid, phthalic acid, terephthalic acid, andpimelic acid.
 3. The mill base composition according to claim 1 whereinthe mill base comprises about 30% to about 60% by weight of the divinylester.
 4. The mill base composition according to claim 1 wherein thedispersing agent is selected from the group consisting of polyesters,polyurethanes, and polyalkylene imines.
 5. The mill base compositionaccording to claim 1 wherein the dispersing agent is present in anamount of about 5% to about 50% by weight of the mill base composition.6. The mill base composition according to claim 1 wherein the dispersingagent further comprises an organic solvent in an amount of about 30% toabout 50% by weight of the dispersing agent.
 7. The mill basecomposition according to claim 6 wherein the organic solvent is selectedfrom the group consisting of acetates, glycols, and combinations ofacetates and glycols.
 8. The mill base composition according to claim 1wherein the dispersing agent further comprises a (meth)acrylic monomerin an amount of about 30% to about 50% by weight of the dispersingagent.
 9. The mill base composition according to claim 8 wherein the(meth)acrylic monomer is selected from the group consisting of2-phenoxyethyl acrylate, isophoryl acrylate, isodecyl acrylate, tridecylacrylate, lauryl acrylate, 2-(2-ethoxy-ethoxy)ethyl acrylate,tetrahydrofurfuryl acrylate, isobornyl acrylate, propoxylated acrylate,tetrahydrofurfuryl methacrylate, 2-phenoxyethyl methacrylate, isobornylmethacrylate, and combinations of two or more thereof.
 10. The mill basecomposition according to claim 1 wherein the pigment is present in anamount of about 10% to about 70% by weight of the mill base.
 11. A UVcurable ink composition comprising: an ink vehicle, and the mill basecomposition according to claim 1 wherein the mill base composition hasbeen subjected to milling.
 12. The UV curable ink composition accordingto claim 11 wherein the ink vehicle comprises one or more of a UVcurable agent, a UV initiator, a surfactant and a UV stabilizing agent.13. A method of preparing a mill base composition, said methodcomprising: (a) providing in combination a compound comprising a divinylester of a dicarboxylic acid wherein the dicarboxylic acid comprisesfrom 2 to about 8 carbon atoms, a dispersing agent, a pigment, andmilling beads; and (b) subjecting the combination to milling.
 14. Themethod according to claim 13 wherein (a) and (b) are repeated one ormore times using milling beads of decreasing diameter.
 15. A UV curableink composition, the composition comprising: (a) a pigment concentratethat is a milled mill base composition, the mill base compositioncomprising (i) a compound comprising a divinyl ester of a dicarboxylicacid wherein the dicarboxylic acid comprises from 2 to about 8 carbonatoms, (ii) a dispersing agent, and (iii) a pigment; (b) one or more UVcurable monomers; and (c) one or more UV initiators.